A Radio Antenna Alignment Tool

ABSTRACT

A radio antenna alignment tool ( 100 ) for aligning a first antenna with respect to at least a second antenna is disclosed. The tool comprises a sensor unit ( 120 ) disposed in connection to the first antenna ( 110 ) comprising means to determine a present direction of the first antenna ( 110 ). The radio antenna alignment tool ( 100 ) further comprises guiding means ( 130 ) adapted to receive, on a first input port, the present direction of the first directive antenna ( 110 ) from the sensor unit ( 120 ). The guiding means ( 130 ) is further arranged to indicate to a user at least one of: the present direction of the first directive antenna ( 110 ), the location of the second antenna, and a preferred direction of the first directive antenna, where said preferred direction of the first directive antenna is determined in order to maximize a signal quality metric for communication between the first directive antenna and at least the second antenna. The tool facilitates the alignment of the first directive radio antenna without the user having direct visual contact with the far end antenna.

TECHNICAL FIELD

The present disclosure relates to alignment of directive radio antennas.

BACKGROUND ART

Directive radio antennas are antennas which concentrate radiated signal energy in one or several pre-determined directions in order to increase the transmitted signal power in that or those directions. The direction in which the most energy is radiated, i.e., the direction with highest antenna gain, is often referred to as the main lobe of the radio antenna. Due to reciprocity, antenna gain characteristics for transmission and reception are often similar in terms of antenna directivity. I.e., the direction of the transmit main lobe as a rule coincides with the direction of the receive main lobe. Examples of directive radio antennas comprise disc antennas, horn antennas, and various forms of antenna arrays.

Directive antennas are an integral part in microwave radio links used for point to point communication, e.g., in cellular backhaul applications. Microwave links as a rule have highly directive antennas at both ends of the radio link. Due to the high directivity, correct alignments of antennas are crucial in order to reach expected performance in a radio link application, as an erroneous alignment will adversely affect system gain. In radio links, and also throughout this text, the directive antenna which is closest to an observer is referred to as the near end antenna, while the second antenna is referred to as the far end antenna. Hence, the antenna which is being aligned is often the near end antenna, which is being aligned with respect to the far end antenna.

When a directive radio antenna is deployed in line-of-sight, LOS, conditions, meaning that there is a clear line of sight between the near end antenna and far end antenna, antenna alignment can be done by visual means, i.e., by visually observing the position of the far end antenna and aligning accordingly. However, in case the communication system is deployed in non-line-of-sight, NLOS, conditions, meaning that the LOS is in some way obstructed, coarse radio antenna alignment can be complicated since the view of the far end antenna is obstructed. In such cases it can be difficult to know how to align the antenna since the direction of the far end antenna is unknown. NLOS radio link deployment is regularly needed for backhaul of small and dense cell deployments in urban cellular networks.

Thus, in order to facilitate quick and cost effective installation of directive radio antennas in NLOS conditions, improvements in radio antenna alignment tools and procedures are needed.

SUMMARY

An object of the present disclosure is to provide a method and a tool for alignment of radio antennas in non-line-of-sight, NLOS, conditions which seeks to mitigate, alleviate, or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and to provide a quick and cost effective means for directive antenna alignment in NLOS conditions.

This object is obtained by a radio antenna alignment tool for aligning a first directive antenna with respect to at least a second antenna. The radio antenna alignment tool comprises a sensor unit disposed in connection to the first directive antenna, the sensor unit comprising means to determine a present direction of the first directive antenna, as well as an interface on which sensor information comprising the present direction can be accessed.

The radio antenna alignment tool further comprises guiding means adapted to receive, on a first input port, the present direction of the first directive antenna from the interface of the sensor unit. The guiding means is also arranged to indicate to a user at least one of: the present direction of the first directive antenna, the location of the second antenna, and a preferred direction of the first directive antenna, where said preferred direction of the first directive antenna is determined in order to maximize a signal quality metric for communication between the first directive antenna and at least the second antenna.

Hence, a user of the tool can look to the guiding means during antenna alignment in order to discern information which facilitates the alignment of the first directive radio antenna without the user having direct visual contact with the far end antenna towards which the first directive antenna should be directed. Thus a quick and cost effective means for directive antenna alignment in NLOS conditions is provided.

According to an aspect, said preferred direction of the first directive antenna is determined in order to maximize the signal quality metric for communication between the first directive antenna and the second antenna in non-line-of-sight, NLOS, conditions.

According to an aspect, the sensor unit further comprises at least one out of a camera, a positioning system unit, a three-dimensional compass, and a radar transceiver unit.

According to an aspect, the camera is adapted to capture an image, and the guiding means is arranged to determine the preferred direction of the first directive antenna by means of processing image data received from the sensor unit.

According to an aspect, the guiding means also comprises a processing unit arranged to receive at least one out of: sensor information data from the sensor unit on a first port of the guiding means, received signal strength data from a radio receiver unit connected to the first directive antenna, and geographic data, which geographic data comprises at least one out of: building coordinates, coordinates of the first directive antenna, coordinates of the second antenna, and geometry of buildings. The processing unit is adapted to determine the preferred direction based on said received data.

According to an aspect, the guiding means also comprises a display unit adapted to display at least one out of: a first indicator indicating the present direction of the first directive antenna, a second indicator indicating the location of the second antenna, and a third indicator indicating the preferred direction of the first directive antenna, thus facilitating alignment of the first directive antenna.

According to an aspect, the display unit is further adapted to display an image showing a camera view as seen from the first directive antenna, in the current direction of the first directive antenna.

According to an aspect, the radio antenna alignment tool is further adapted to determine a plurality of preferred directions of the first directive antenna with respect to the second antenna, which preferred directions are suitable for communication over an NLOS communication channel where an obstacle blocks the line-of-sight, LOS, between the first directive antenna and the second antenna, by evaluating a plurality of alternative propagation paths, including propagation paths with reflection and propagation paths with diffraction.

According to an aspect, the radio antenna alignment tool further comprises an emitter unit disposed in connection to the second antenna. The emitter unit is arranged to transmit a known signal. The sensor unit is adapted to receive said known signal, as well as to measure the power of the received known signal. The guiding means is arranged to receive said power measurement value from the sensor unit, and to indicate said power measurement value to a user, as well as to determine the preferred direction of the second directive antenna based on said power measurement value.

According to an aspect, the emitter unit and sensor unit also comprises first and second antenna arrays, respectively. The emitter unit is arranged to transmit a known narrow-beam signal in a pre-determined sequence over a first pre-determined range of antenna array beam transmit directions. The sensor unit is arranged to measure received signal power over a second pre-determined range of antenna array beam receive directions, as well as to communicate said power measurements and corresponding receive beam directions to the guiding means. The guiding means is arranged to store said power measurements together with the corresponding receive beam directions in a memory, and to select a suitable direction of the first directive antenna based on said received power measurements and corresponding receive beam directions.

The above stated object is also obtained by means of a method for aligning a first directive antenna and at least a second antenna in non-line-of-sight, NLOS, communication conditions. The method comprising the steps of;

-   -   Sensing a current direction of the first directive antenna,     -   Determining a preferred direction of the first directive         antenna, which preferred direction maximizes a signal quality         metric for communication between the first and second antenna,     -   Presenting to a user at least one out of: the current direction         of the first directive antenna, the location of the second         directive antenna, the preferred direction of the first         directive antenna.

Thus, the disclosed tool and method for antenna alignment will simplify the installation of directive radio antennas used, e.g., in wireless NLOS backhaul radio links. By reducing alignment time, and also relaxing requirements on installer expertise, an efficient and cost effective roll-out of radio link networks is facilitated. These are important benefits, especially when it comes to the deployment of radio link backhaul for small and dense cell deployment in urban cellular networks.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technique will be described in more detail in the following, with reference to the appended drawings, in which

FIG. 1 shows a first aspect of a radio antenna alignment tool, and

FIG. 2 shows a second aspect of a radio antenna alignment tool, and

FIG. 3 shows a display unit, and

FIG. 4 shows a third aspect of a radio antenna alignment tool, and

FIG. 5 shows a flowchart of a method of the disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which different aspects of the disclosure are shown. The present technique may, however, be embodied in many different forms and should not be construed as being limited to those aspects set forth herein. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the technique to those skilled in the art. Like reference signs refer to like elements throughout the description.

FIG. 1 shows a first aspect of a radio antenna alignment tool 100. The alignment tool 100 comprises a sensor unit 120 which has been attached to a first directive antenna 110. The antenna 110 shown in FIG. 1 is a disc antenna, but other types of directive antennas are possible to use, e.g., a horn antenna or an antenna array. The antenna 110 can also be part of a group of antennas constituting a multiple antenna system, e.g., a multiple-input multiple-output, MIMO, antenna system. The first directive antenna 110 is suitably attached to fixed infrastructure, here shown as a mast pole 150, by means of an attachment device 140. The attachment device 140 suitably allows for changing the direction of the antenna 110. Thus, by means of the attachment device 140 the alignment of the directive antenna 110 can be changed, either manually or automatically by means of, e.g., an electric motor.

The first directive antenna 110 is directive in the sense that it transmits and receives electromagnetic energy with higher gain in some directions compared to other directions. The direction of largest gain is referred to as the main lobe of the antenna. Henceforth, when referring to a direction, e.g., a preferred direction, in relation to a directive antenna, it is the direction of the antenna main lobe which is referred to.

The sensor unit 120 comprises means to determine in which direction the first directive antenna 110 is directed. As will be explained in more detail below, the sensor unit 120 in aspects of the tool 100 comprises a number of different sensors, sensing a wide range of information which could be of assistance to a user of the tool 100 in the alignment process. The sensor unit 120 further comprises an interface 121 on which sensor information can be accessed. This interface 121 is not necessarily an electrical or optical data interface: A display where a user can read information visually is used as interface 121 in various aspects of the tool 100.

The tool 100 further comprises guiding means 130 connected to the interface 121 of the sensor unit 120 via a first port 131 of the guiding means 130. The guiding means 130 suitably comprises information processing and visualization means in order to assist a user of the tool with aligning the first directive radio antenna 110. Aspects of the guiding means 130 will be described in more detail in connection to FIG. 3 below.

Consequently, FIG. 1 shows a radio antenna alignment tool 100 for aligning a first directive antenna 110 with respect to at least a second antenna. The radio antenna alignment tool 100 comprises a sensor unit 120 disposed in connection to the first directive antenna 110, the sensor unit 120 comprising means to determine a present direction of the first directive antenna 110, as well as an interface 121 on which sensor information comprising the present direction can be accessed.

The radio antenna alignment tool 100 further comprises guiding means 130 adapted to receive, on a first input port 131, the present direction of the first directive antenna 110 from the interface 121 of the sensor unit 120. The guiding means 130 is also arranged to indicate to a user at least one of: the present direction of the first directive antenna 110, the location of the second antenna, and a preferred direction of the first directive antenna 110, where said preferred direction of the first directive antenna 110 is determined in order to maximize a signal quality metric for communication between the first directive antenna 110 and at least the second antenna.

Hence, a user of the system employs the guiding means 130 in order to discern crucial information needed to align the first directive antenna 110 without having direct visual contact with the far end antenna towards which the first directive antenna 110 should be directed. In fact, a user of the tool 100 does not even need to know approximately where the far end antenna is located as this information is communicated to him via said guiding means 130.

It should be noted that the preferred direction of the first directive antenna 110 is not necessarily directly towards the far end antenna. The preferred direction depends on propagation conditions in the particular communications scenario. Thus, the preferred direction can be towards a point where a strong reflection of radio energy occurs, or towards a point where a diffraction of radio energy occurs, or even towards a point which is preferred due to a combination of propagation phenomena working together to make the direction a preferred direction.

In aspects of the tool 100, the signal quality metric comprises an estimate or measure of received signal power, or, alternatively, an estimate or measure of received signal energy. The received signal in question being received by the first directive antenna 110 from the far end antenna or alternatively from a third antenna located in the immediate vicinity of the far end antenna.

Concrete examples of the signal quality metric, which metric is maximized by pointing the first directive antenna 110 in the preferred direction, will be given below. This signal quality metric takes on different forms in various aspects of the tool 100, depending on, e.g., the communication system hardware. Signal quality metrics are in different aspects of varying complexity ranging from low complexity metrics such as received signal strength, RSS, i.e., received signal energy or received signal power, to more advanced signal quality metrics such as mutual information metrics and other similar information theoretic measures of received signal quality.

Signal quality metrics based on the detection of a communication signal, e.g., a quadrature amplitude modulated, QAM, signal, by means of a communications receiver are of course also possible to use. Examples of such signal quality metrics include the mean squared error, MSE, and the signal to noise ratio, SNR, as well as the amount of frequency selectivity in the propagation channel. MSE can be measured as the squared difference between a received signal and a detected or a known signal, SNR can be measured by comparing received signal power to receiver noise power, and the frequency selectivity of a propagation channel can be measured by analysis of the filter transfer function of an equalizer comprised in the receiver. The bit error rate, BER, and frame error rate, FER, in a detected communication signal are of course viable signal quality metrics as well. It should be noted that the determining of above-mentioned signal quality metrics can be facilitated by a transmission of known pilot symbols from the far end to the near end installations.

Thus, according to an aspect, the signal quality metric used for aligning the first directive antenna 110 in the preferred direction comprises at least one out of a received signal power, a mean squared error, a measure of frequency selectivity, a bit error rate, and a frame error rate, measured on a signal received by the first directive antenna 110 from at least the second antenna.

According to an aspect, the preferred direction of the first directive antenna 110 is determined in order to maximize a signal quality metric for communication between the first directive antenna 110 and the second antenna in non-line-of-sight, NLOS, conditions. An example of this is if the communication system is a multi-antenna communication system. In such cases the communication channel rank or condition number is likely to be of importance. Hence, channel quality metrics related to multi-antenna systems, e.g., multiple-input multiple-output, MIMO, systems, such as channel rank and channel condition number, is in aspects of the tool 100 comprised in the signal quality metric.

A common trait in all signal quality metrics mentioned above which can be considered for use in aspects of the disclosed system 100 is that they in some way indicate the quality or expected quality of the signal received at the first directive antenna 110, or at a second far end antenna. Thus, the better the antenna alignment is, the higher the signal quality metric becomes.

FIG. 2 shows a second aspect of a radio antenna alignment tool 200. A non-line-of-sight, NLOS, radio link is to be established between a far end radio unit 240 and a near end radio unit 230, which near end radio unit 230 transmits and receives by means of a first directive radio antenna 110. In order to have the radio link functional, the first directive radio antenna 110 must be carefully aligned such as to enable communication between near end 230 and far end 240 radio units. A sensor unit 120 is disposed in connection to the first directive radio antenna 110. In this aspect of the tool 200, the sensor unit 120 comprises a plurality of sensors: A positioning unit 222, a 3D-compass 221, a radar transceiver unit 223, and a camera 220.

The positioning unit 222 is suitably a global positioning system, GPS, receiver, a Galileo positioning system receiver, a Glonass receiver, or similar positioning system receiver. The positioning system is arranged to determine the coordinates, i.e., the position, of the first directive antenna 110. Information from said sensors is made available, i.e., is adapted to be transmitted, via the sensor unit interface 121. Thus, by connecting to the interface 121, the coordinates of the near end antenna, the 3D direction of the near-end antenna, a radar image of the surrounding environment, and an image of the surrounding environment can be accessed.

The radio antenna alignment tool 200 further comprises guiding means 130. The guiding means 130 accesses the sensor information listed above by connecting to the sensor unit interface 121 via a first input port 131 of the guiding means 130. The guiding means 130 also comprises a second input port 212, on which second input port 212 the guiding means is arranged to receive signal strength data from the near end radio unit 230, i.e., a measure of the signal strength of a signal received from the far end radio unit 240. Further, the guiding means 130 comprises a third input port 211 on which external input data is received. Examples of such external input data are geographic data, which geographic data in different aspects of the tool 200 comprises at least one out of: building coordinates, pre-determined coordinates of the first directive antenna 110, pre-determined coordinates of the far end radio unit 240, pre-determined coordinates of the antenna of the far end radio unit, and geometry of buildings in the vicinity of the radio link.

The inputs to the first 131, second 212, and third 211 input ports are received by a processing unit 210. The processing unit 210 is arranged to process the sensor information and external data in order to determine a preferred direction of the first directive radio antenna 110. The preferred direction is in different aspects of the tool 200 determined by interpolation between geographical coordinates, or by means of propagation models of the surrounding environment.

Thus, FIG. 2 shows an aspect of the tool 200 wherein the sensor unit 120 comprises at least one out of a camera 220, a positioning system unit 222, a two-dimensional compass (not shown in FIG. 2), a three-dimensional compass 221, and a radar transceiver unit 223.

The processing unit 210 is connected to a display unit 132, which will be described in detail in connection to FIG. 3 below.

According to an aspect of the tool 200, the sensor unit 120 comprises a camera 220 adapted to capture an image, and the guiding means 130 is arranged to determine the preferred direction of the first directive antenna 110 by means of processing image data received from the sensor unit 120. A number of image processing techniques can be employed for this purpose. As an example, the location in the captured image of the far end antenna is estimated based on an input location of the far end antenna, or simply input by the user. The preferred direction is then determined by means of interpolation between the location in the image of the far end antenna and the location of the camera 220.

Thus, the disclosed alignment tool 200 can aid in visualizing the current alignment of the first directive radio antenna 110, and supports the installer by determining and visualizing a preferred direction of the first directive antenna 110, e.g., by projecting an aiming sight indicating the preferred direction or the location of the far end antenna onto the captured image. The location of the far end antenna can be programmed into the guiding means 130 prior to installation or down-loaded on-site. The user of the tool 200 can then change the alignment of the first directive antenna 110 such that the current direction of the antenna coincides with the preferred direction.

According to another aspect, the guiding means 130 comprises a processing unit 210 arranged to receive at least one out of: sensor information data from the sensor unit 120 on the first port 131 of the guiding means 130, received signal strength data from a radio receiver unit 230 connected to the first directive antenna 110, and geographic data. The geographic data comprises at least one out of: coordinates of surrounding buildings, coordinates of the first directive antenna 110, coordinates of the second antenna, and information pertaining to the geometry of surrounding buildings.

The processing unit 210 is in aspects of the tool 200 adapted to determine the preferred direction based on said received data. This means that the processing unit 210 can determine the geographical and electromagnetical layout of the current link between the first directive antenna 110 and the second antenna. Then, based on this information the processing unit 210 determines a direction in which to direct the near end antenna in order to maximize a signal quality metric. An example of this is to apply ray-tracing techniques based on an emitted signal from the far end antenna, which simulates the propagation of the emitted signal based on the propagation environment, in order to determine the preferred direction of the near end antenna in which the most signal energy is inbound. A less complex alternative aspect is to, as mentioned above, apply a linear interpolation between the position of the far end antenna and the position of the near end antenna, and to base the preferred direction upon said interpolation.

In aspects of the tool, the determining of preferred direction is an iterative process, i.e., the guiding means 130 instructs the user to change the current direction upon which the sensor unit 120 makes additional measurements of e.g., received signal power. In this way a range of directions can be scanned in order to determine which direction that gave the optimum signal quality metric. The guiding means 130 suitably then instructs the user to direct the near end antenna, i.e., the first directive antenna 100, in the direction of highest signal quality metric.

Thus, input data to the processing unit 210 is first used to determine a coarse alignment by means of image processing and geometrical methods, following which a fine alignment is performed.

FIG. 3 shows a display unit 132 suitable for use in a guiding means. The display unit 132 can perform the function of interfacing with a user of the radio antenna alignment tool 100. In this aspect of the display unit 132, the display unit 132 comprises a display or screen 332 on which an image as seen from the camera 220 of the sensor unit 120 can be displayed. Alternatively, in other aspects of the display unit 132, no camera image is displayed on the screen 332, which instead shows a background image, possibly monochrome.

At least three indicators are in aspects displayed to the user on the screen 332; a first indicator 333 indicating the present direction of the first directive antenna 110, a second indicator 334 indicating the location of the second antenna, and a third indicator 335 indicating a preferred direction of the first directive antenna 110.

Thus, a user of the tool can look to the display unit 132 and receive information which facilitates the alignment of the first directive radio antenna 100. In this way, the user of the tool will know at least approximately where the far end radio unit and far end antenna unit is located, and how to direct the first directive antenna 110 to achieve radio link connectivity, even though there is no clear line of sight between the near end installation and the far end installation of the radio link.

It should be noted that the display unit can take on many alternative forms in aspects of the guiding means 130, such as a simple arrangement of diodes, or audio means which indicate a preferred direction by playing a sound to the user.

Consequently, the guiding means 130 comprises a display unit 132 adapted to display at least one out of: a first indicator 333 indicating the present direction of the first directive antenna, a second indicator 334 indicating the location of the second antenna, and a third indicator 335 indicating the preferred direction of the first directive antenna 110, thus facilitating alignment of the first directive antenna 110.

According to an aspect, the display unit 132 is further adapted to display an image showing a camera view as seen from the first directive antenna 110, in the current direction of the first directive antenna 110.

Of course, the display unit can take on many forms in different aspects of the alignment tool. One example as noted above being a visual display unit which displays an image captured by a camera, in which image the location of the far end antenna and the preferred direction have been marked by visual indicators, another example being a display unit which shows one or several direction indicators, possibly in the shape of arrows, which point in the direction of the far end antenna and in the preferred direction. An even simpler display unit would just comprise one or several light emitting diodes, LEDs, which guides the user to direct the first directive antenna in a preferred direction, the preferred direction suitably being indicated by a pre-determined LED.

FIG. 4 shows a non-line-of-sight, NLOS, communication channel with first 110 and second 410 antennas. The channel between the first 110 and second 410 antenna is blocked by obstacles 420, 421. However, radio signals transmitted from, e.g., the second antenna 410 can still reach the first antenna 110 by means of reflection 422 or diffraction 423. It is also noted that in this aspect there are at least two preferred directions of the first directive radio antenna 110. The tool for radio antenna alignment is in this aspect constructed such as to provide a user with a plurality of alternative preferred directions. The user of the tool can then select between the preferred directions when mounting the antenna. In case of a plurality of preferred directions, the guiding means is suitably adapted to display each of these preferred directions to a user of the tool, possibly by means of additional indicators on the display unit 132 of the guiding means 130.

Thus, the radio antenna alignment tool 400 is adapted to determine a plurality of preferred directions of the first directive antenna 110 with respect to the second antenna 410, which preferred directions are suitable for communication over an NLOS communication channel where an obstacle 420, 421 blocks the line-of-sight, LOS, between the first directive antenna 110 and the second antenna 410, by evaluating a plurality of alternative propagation paths, including propagation paths with reflection 422 and propagation paths with diffraction 423.

The user is in the present aspect given a plurality of different alternatives in which to direct the first directive antenna 110. This could be beneficial in cases where some directions are difficult to achieve for practical reasons, e.g., due to the mounting of the first directive antenna 110. For instance, the mounting of the antenna could be such as to not allow certain antenna angles.

According to an aspect, the radio antenna alignment tool 400 also comprises an emitter unit 430 disposed in connection to the second antenna 410, the emitter unit 430 is arranged to transmit a known signal. The sensor unit 120 is in this case adapted to receive the known signal, as well as to measure the power of the received known signal. The guiding means 130 is further arranged to receive said power measurement value from the sensor unit 120, and to indicate said power measurement value to a user of the tool, as well as to determine the preferred direction of the first directive antenna 110 based on said power measurement value.

The emitter unit 430 suitably uses an isotropic antenna or an antenna with a less narrow main lobe compared to the first directive antenna 110, such that a signal can be received from the emitter despite poor alignment of the emitter antenna with respect to the first directive antenna 110.

According to an aspect, the emitter unit 430 and sensor unit 120 further comprises first and second antenna arrays, respectively. The emitter unit 430 is in this aspect arranged to transmit a known narrow-beam signal in a pre-determined sequence over a first pre-determined range of antenna array beam transmit directions. The sensor unit 120 is arranged to measure received signal power over a second pre-determined range of antenna array beam receive directions, as well as to communicate said power measurements and corresponding receive beam directions to the guiding means 130. The guiding means 130 is arranged to store said power measurements together with the corresponding receive beam directions in a memory, and to select a suitable direction of the first directive antenna 110 based on said received power measurements and corresponding receive beam directions.

Thus a range of transmit and receive direction combinations can be scanned automatically, and a user can quickly evaluate a range of possible alignment options and select a promising direction of both the near end antenna and the far end antenna. This is suitable in cases of complicated propagation conditions where it is difficult to calculate or otherwise determine a preferred direction by means of, e.g., image processing or ray tracing techniques.

FIG. 5 shows a flowchart of a method for aligning a first directive antenna and at least a second antenna in non-line-of-sight, NLOS, communication conditions. The method comprising the steps of;

-   -   Sensing 510 a current direction of the first directive antenna,     -   Determining 520 a preferred direction of the first directive         antenna, which preferred direction maximizes a signal quality         metric for communication between the first and second antenna,     -   Presenting 530 to a user at least one out of: the current         direction of the first directive antenna, the location of the         second directive antenna, the preferred direction of the first         directive antenna.

According to an aspect, the step of sensing 510 further comprises sensing at least one out of a camera image as seen from the first directive antenna, the coordinates of the first directive antenna, and the coordinates of the second directive antenna.

According to an aspect, an emitter is disposed in connection to the second directive antenna and arranged to transmit a known radio signal, and the step of sensing 510 further comprises measuring a received signal power by means of a radio receiver unit connected to the first directive radio antenna and adapted to receive the known radio signal.

According to an aspect, the step of determining 520 further comprises determining the preferred direction to maximize the signal quality metric based on at least one out of: the result from the step of sensing, a measurement of received signal power, and map information, which map information comprises pre-determined building coordinates, antenna unit coordinates, and building geometry.

The above stated object of the disclosure is further obtained by a computer program for assisting in aligning a first directive antenna 110 with respect to at least a second antenna. The computer program, when executed by a processor of a mobile device, causes the mobile device to perform any one of the methods disclosed herein.

The above stated object of the disclosure is also obtained by a mobile device for assisting in aligning a first directive antenna 110 with respect to at least a second antenna, comprising a processor, and a storage medium for storing computer programs executable by said processor.

The foregoing has described the principles, preferred aspects and modes of operation of the present disclosure. However, the invention described herein should be regarded as illustrative rather than restrictive, and not as being limited to the particular aspects discussed above. The different features of the various aspects of the disclosure can be combined in other combinations than those explicitly described. It should therefore be appreciated that variations may be made in those aspects by those skilled in the art without departing from the scope of the present disclosure as defined by the following claims. 

1-18. (canceled)
 19. A radio antenna alignment tool for aligning a first directive antenna with respect to at least a second antenna, the radio antenna alignment tool comprising: a sensor unit disposed connected to the first directive antenna, the sensor unit comprising: means to determine a present direction of the first directive antenna; an interface on which sensor information comprising the present direction can be accessed, guiding means configured to: receive, on a first input port, the present direction of the first directive antenna from the interface of the sensor unit; indicate to a user at least one of: the present direction of the first directive antenna, the location of the second antenna, and a preferred direction of the first directive antenna; wherein the preferred direction of the first directive antenna is determined in order to maximize a signal quality metric for communication between the first directive antenna and at least the second antenna.
 20. The radio antenna alignment tool of claim 19: wherein the signal quality metric comprises at least one parameter of: a received signal power; a mean squared error; a measure of frequency selectivity; a bit error rate; a frame error rate; a multiple-antenna communication channel rank; and a multiple-antenna communication channel condition number; wherein the parameter is measured based on a signal received at the first directive antenna from at least the second antenna.
 21. The radio antenna alignment tool of claim 19, wherein the preferred direction of the first directive antenna is determined in order to maximize the signal quality metric for communication between the first directive antenna and the second antenna in non-line-of-sight (NLOS) conditions.
 22. The radio antenna alignment tool of claim 19, wherein the sensor unit further comprises at least one of: a camera; a positioning system unit; a three-dimensional compass; and a radar transceiver unit.
 23. The radio antenna alignment tool of claim 19: wherein the sensor unit comprises a camera adapted to capture an image; wherein the guiding means is configured to determine the preferred direction of the first directive antenna by means of processing image data received from the sensor unit.
 24. The radio antenna alignment tool of claim 19: wherein the guiding means further comprises a processing circuit configured to receive at least one of: sensor information data from the sensor unit on the first port of the guiding means; received signal strength data from a radio receiver unit connected to the first directive antenna; geographic data; wherein the geographic data comprises at least one of: building coordinates; coordinates of the first directive antenna; coordinates of the second antenna; and geometry of buildings; wherein the processing circuit is configured to determine the preferred direction based on the received data.
 25. The radio antenna alignment tool of claim 19, wherein the guiding means further comprises a display unit configured to display at least one of: a first indicator indicating the present direction of the first directive antenna; a second indicator indicating the location of the second antenna; a third indicator indicating the preferred direction of the first directive antenna.
 26. The radio antenna alignment tool of claim 25, wherein the display unit is further configured to display an image showing a camera view as seen from the first directive antenna, in the current direction of the first directive antenna.
 27. The radio antenna alignment tool of claim 19: wherein the radio alignment tool is configured to determine a plurality of preferred directions of the first directive antenna with respect to the second antenna, the preferred directions being suitable for communication over an non-line-of-sight (NLOS) communication channel where an obstacle blocks a line-of-sight (LOS), between the first directive antenna and the second antenna, wherein the radio alignment tool is configured to determine the plurality of preferred directions by evaluating a plurality of alternative propagation paths, including propagation paths with reflection and propagation paths with diffraction.
 28. The radio antenna alignment tool of claim 19: further comprising an emitter unit connected to the second antenna, the emitter unit being configured to transmit a known signal; wherein the sensor unit is configured to receive the known signal and to measure the power of the received known signal; wherein the guiding means is configured to: receive the power measurement value from the sensor unit; indicate the power measurement value to a user; determine the preferred direction of the first directive antenna based on the power measurement value.
 29. The radio antenna alignment tool of claim 28: wherein the emitter unit and sensor unit each comprise first and second antenna arrays, respectively; wherein the emitter unit is configured to transmit a known narrow-beam signal in a pre-determined sequence over a first pre-determined range of antenna array beam transmit directions; wherein the sensor unit is configured to measure received signal power over a second pre-determined range of antenna array beam receive directions, wherein the sensor unit is configured to communicate the power measurements and corresponding receive beam directions to the guiding means; wherein the guiding means is configured to: store the power measurements together with the corresponding receive beam directions in a memory; select a suitable direction of the first directive antenna based on the received power measurements and corresponding receive beam directions.
 30. A method for aligning a first directive antenna and at least a second directive antenna in non-line-of-sight (NLOS) communication conditions, the method comprising: sensing a current direction of the first directive antenna; determining a preferred direction of the first directive antenna, the preferred direction maximizing a signal quality metric for communication between the first and second antennas; presenting, to a user, at least one of: the current direction of the first directive antenna; the location of the second directive antenna; the preferred direction of the first directive antenna.
 31. The method of claim 30: wherein the signal quality metric comprises at least one parameter of: a received signal power; a mean squared error; a measure of frequency selectivity; a bit error rate; a frame error rate; a multiple-antenna communication channel rank; a multiple-antenna communication channel condition number; wherein the parameter is measured based on a signal received at the first directive antenna from at least the second antenna.
 32. The method of claim 30, wherein the sensing the current direction of the first directive antenna comprises sensing at least one of: a camera image as seen from the first directive antenna; coordinates of the first directive antenna; coordinates of the second directive antenna.
 33. The method of claim 30: wherein an emitter is connected to the second directive antenna and configured to transmit a known radio signal; wherein the sensing the current direction of the first directive antenna comprises measuring a received signal power by means of a radio receiver unit, connected to the first directive radio antenna, that is configured to receive the known radio signal.
 34. The method of claim 33, wherein the determining a preferred direction of the first directive antenna comprises determining the preferred direction to maximize the signal quality metric based on at least one of: the result from the sensing the current direction of the first directive antenna; a measurement of received signal power; map information, the map information comprising pre-determined building coordinates, antenna unit coordinates, and building geometry.
 35. A computer program product stored in a non-transitory computer readable medium for assisting in aligning a first directive antenna with respect to at least a second directive antenna in non-line-of-sight (NLOS) communication conditions, the computer program product comprising software instructions which, when run on one or more processors of a mobile device, causes the mobile device to: sense a current direction of the first directive antenna; determine a preferred direction of the first directive antenna, the preferred direction maximizing a signal quality metric for communication between the first and second antennas; present, to a user, at least one of: the current direction of the first directive antenna; the location of the second directive antenna; the preferred direction of the first directive antenna.
 36. A mobile device for assisting in aligning a first directive antenna with respect to at least a second directive antenna in non-line-of-sight (NLOS) communication conditions, the mobile device comprising: a processor, a non-transitory computer readable medium storing software instructions, the software instructions configured to, when run on the processor, cause the mobile device to: sense a current direction of the first directive antenna; determine a preferred direction of the first directive antenna, the preferred direction maximizing a signal quality metric for communication between the first and second antennas; present, to a user, at least one of: the current direction of the first directive antenna; the location of the second directive antenna. 